Various proposals have been made for replacing the conventional hydraulic shock absorber and exterior coil spring assemblies in vehicular suspension systems with more compact devices known as liquid springs. A conventional liquid spring includes a cylindrical housing having an internal chamber with a compressible liquid therein, a piston reciprocally disposed in the chamber, a rod structure secured to the piston and axially movable into and out of the chamber, and having an external strut projecting outwardly of one of the housing ends. With the liquid spring operatively interconnected between the vehicle frame and an associated wheel support structure, the compressible working liquid generates both spring and damping forces in the suspension system in response to relative axial translation between the rod structure and housing of the liquid spring caused by relative vertical displacement between the wheel and the frame.
The compressible working liquid permits the system to exhibit a non-linear force/deflection curve. This non-linear behavior is important because it offers lower spring rates during normal operation and higher spring rates when the vehicle strikes a bump. Non-linearity in the system is provided by the compressibility of the silicone-based working liquid, which is approximately 1.5 to 2 times more compressible than conventional hydraulic fluid. In operation, the non-linear system provides a spring rate which increases exponentially when the strut moves from its normal static position to full compression. This increase permits the suspension unit to absorb sharp bumps without bottoming out. In contrast, if the spring rate were linear, a substantially greater piston stroke would be required to enable the suspension unit to absorb comparable bounce forces.
Conventional liquid spring suspensions can be tuned and readily adjusted for differing vehicle weights (springing force) and different ride characteristics (dampening). It will be appreciated that non-linear struts that utilize a compressible working liquid for both springing and dampening have a potential for superior performance.